Controlled Radical Polymerization, and Catalysts Useful Therein

ABSTRACT

A catalyst is prepared in situ by reaction between an aryl halide and a Ni-ligand complex. The catalyst may be used to promote chain-growth polymerization of halogen-substituted Mg or Zn monomers. Polymers, copolymers, block copolymers, polymer thin films, and surface-confined polymer brushes may be produced using the catalyst.

This is a divisional of application Ser. No. 14/126,514, filing dateDec. 16, 2013, now U.S. Pat. No. 9,644,072; which is the United Statesnational stage of international application PCT/US2012/044530, filingdate Jun. 28, 2012; which claims the benefit of the Jul. 1, 2011 filingdate of U.S. provisional patent application Ser. No. 61/503,727 under 35U.S.C. §119(e). The complete disclosures of each of these priorapplications are hereby incorporated by reference in their entirety.

This invention was made with support from the United States Governmentunder grants CHE-0547895 and DMR-1006336 awarded by the National ScienceFoundation. The United States Government has certain rights in thisinvention.

TECHNICAL FIELD

Conjugated polymers, particularly polythiophenes (PTs) are widely usedin electronics and optoelectronics (e.g., thin-film transistors,photovoltaic cells, polymeric light-emitting diodes), as well as inchemosensing and biosensing devices. There is an unfilled need for newPTs, polythiophene copolymers, and other conjugated polymers havingproperties that can be fine-tuned to meet the requirements of particularapplications; for improved methods of synthesizing PTs and theircopolymers; and for improved catalysts suitable for catalyzing suchsyntheses and in catalyzing related reactions.

BACKGROUND ART

“Living polymerization” is a form of addition polymerization in whichchain termination reactions are absent or are strongly inhibited.Polymer chains typically grow at a more constant rate in livingpolymerization than is seen in other types of polymerization, and theresulting chain lengths tend to be similar (i.e., the polymers have avery low polydispersity index). Living polymerization is useful forsynthesizing block copolymers. A block copolymer can be synthesized intwo or more stages, with each stage containing a different monomer.

One method that has been used for preparing PTs and their blockcopolymers is living polymerization based on the Ni-catalyzed Kumadapolymerization of 5-bromo-2-thienylmagnesium monomers. Mechanisticstudies have suggested that this polymerization proceeds through acyclic catalysis mechanism involving a series of oxidativeaddition/reductive elimination steps. To take full advantage of the“living” polymerization mechanism, the reaction is typically conductedat ambient temperature. The reaction generally yields polymers havinglow to medium molecular weights due to the low reactivity of the Ni(II)catalysts that have been used, such as Ni(dppp)Cl₂ (where dppp is1,3-bis(diphenylphosphino)propane). The Ni center typically has asquare-planar geometry. However, in this system it is possible for thepropagating Ni(II) reactive center to transfer from one chain to anotherduring polymerization, so this polymerization might more accurately bedescribed as “quasi-living.” True “living” polymerization would beenhanced by the availability of highly reactive universal catalyticsystems.

Prior approaches to preparing regioregular, high molecular weightpoly(3-alkylthiophene)s have required relatively high temperatures andlong reaction times. As a consequence, the resulting polymers have showndecreased regioregularity (85-95%), and despite high reactiontemperatures and long reaction times, have still shown relatively lowmolecular weights. The difficulty in obtaining high-regioregularity(around 100%) polythiophenes in substantial amounts hinders developmentof practical applications of these materials and has prompted somestudies of less-regioregular polythiophenes as possible substitutes.

V. Senkovskyy et al., J. Am. Chem. Soc. 2007, 129, 6626-6632; R. Tkachovet al., J. Am. Chem. Soc. 2010, 132, 7803-7810; and H. Bronstein et al.,J. Am. Chem. Soc. 2009, 131, 12894-12895 reported an externallyinitiated living polymerization process in which a stable aryl-Ni(II)initiating complex, e.g. σ-complex 1 (FIG. 1A), was used to catalyze thepolymerization of Grignard monomer 2. The catalytic initiator wasstabilized by a bidentate phosphine ligand. The initiator was preparedby ligand exchange between the initial complex with monodentatephosphine ligands which, in turn, may be prepared by oxidative additionof an aryl halide to Ni(PPh₃)₄ (FIG. 1A). This external initiation routeenhances the utility of living catalyst-transfer polymerization. Forexample, it makes it possible to grow surface-immobilized PT brushes.However, the previously-reported process requires a relativelycomplicated preparation to make the catalytic initiator; and it ispossible for the initiator to be contaminated with monodentate PPh₃ligand. Any such contamination can decrease catalytic activity, andlimits practical applications of this method.

C. Amatore et al., Organometallics 1988, 7, 2203-2214 reported thatNi(0) complexes containing bidentate phosphine ligands do not react witharyl halides.

T. Yokozawa et al., Chem. Rev. 2009, 109, 5595-5619 provides a reviewsummarizing recent research in chain-growth condensation polymerization.

N. Marshall et al., Chem. Commun., 2011, 47, 5681-5689 provides a reviewsummarizing recent research in surface-initiated polymerization ofconjugated polymers.

M. Iovu et al., Macromolecules 2005, 38, 8649-8656 reported a Grignardmetathesis polymerization of 3-alkylthiophenes by a quasi-living chaingrowth mechanism using a1,3-bis(diphenylphosphino)propane]dichloronickel(II) (Ni(dppp)Cl₂)initiator. The authors reported that the reaction proceeded through acycle of oxidative addition/reductive elimination steps.

R. Miyakoshi et al., J. Am. Chem. Soc. 2005, 127, 17542-17547hypothesized that the mechanism for chain-growth polymerization of2-bromo-5-chloromagnesio-3-hexylthiophene with Ni(dppp)Cl₂ involved acoupling reaction between a Grignard thiophene and the growing polymervia the Ni catalyst, which was transferred intramolecularly to theterminal C—Br bond of the elongated molecule, a mechanism that theauthors called a catalyst-transfer polycondensation. That is, thepolycondensation was said to proceed with the catalyst transferring toand activating the elongated polymer end group.

E. Lanni et al., J. Am. Chem. Soc. 2009, 131, 16573-16579 proposedmechanisms for the Ni(dppe)Cl₂-catalyzed chain-growth polymerization of4-bromo-2,5-bis(hexyloxy)phenylmagnesium chloride and5-bromo-4-hexylthiophen-2-ylmagnesium chloride. Both polymerizationsexhibited first-order dependence on the catalyst concentration, but werenearly independent of the monomer concentration. ³¹P NMR spectroscopicstudies suggested that the resting states were unsymmetricalNi^(II)-biaryl and Ni^(II)-bithiophene complexes. In combination, thedata suggested reductive elimination was the rate-determining step forboth monomers, followed by subsequent intracomplex oxidative addition,leading to chain growth.

V. Senkovskyy et al., J. Am. Chem. Soc. 2007, 129, 6626-6632 described amethod to grow conductive polymer brushes of regioregular head-to-tailpoly(3-alkylthiophene)s via surface-initiated, catalyst-transfer chaingrowth polycondensation of 2-bromo-5-chloromagnesio-3-alkylthiophene.The method used a Ni(II) macroinitiator formed by reaction of Ni(PPh₃)₄with photo-crosslinked poly-4-bromostyrene films. Exposing the initiatorlayers to the monomer solution led to selective chain growthpolycondensation of the monomer onto the surface, thereby producingconductive polymer brushes. The brushes were said to be mechanicallyrobust, and to be stable against delamination.

H. Bronstein et al., J. Am. Chem. Soc. 2009, 131, 12894-12895 reportedthe polymerization of a thiophene Grignard reagent, initiated from anexternally added cis-chloroaryl(dppp) nickel complex, to produce aregioregular poly(3-hexylthiophene) with controlled molecular weightsand narrow polydispersities.

Regioregularity has often been considered to be an important factor inoptimizing the electronic properties of polythiophenes. See, e.g., A.Carella et al., “Synthesis and application to OPV of highly regioregularpolyalkoxyphenylthiophenes catalyzed by copper complexes,” JointItalian-Israeli Workshop on Organic PV, Portici, Italy, Oct. 20, 2011.However, there have also been reports that the regioregularity of thepolymer may not have a significant effect on the power conversionefficiency of a photovoltaic device. See, e.g., R. Mauer et al., Adv.Funct. Mater 2010, 20, 2085-2092.

DISCLOSURE OF THE INVENTION

We have discovered novel catalysts useful in controlled polymerization,for example Compound 4, and an efficient method for preparing the novelcatalysts by the direct oxidative addition of an aryl halide to anickel(0)-containing species such as Ni(dppp)₂ (E.g., FIG. 1B). Thecatalyst facilitates the controlled polymerization of5-bromo-2-thienylmagnesium monomers, as well as the controlledpolymerization of other halogen-substituted Grignard reagent monomers orof halogen-substituted organozinc monomers. The polymerization is highlyefficient. The novel catalyst allows the controlled preparation ofregioregular polythiophenes and block copolymers, as well as otherconjugated polymers such as poly(p-phenylene)s, polyfluorenes, etc. Itmay be used not only to prepare conjugated polymers in solution, butalso to prepare surface-confined films of conjugated polymers. The novelcatalytic initiators are convenient to synthesize, and provide apowerful means to prepare, in highly controlled fashion, polythiophenesand other conjugated polymers with high regioregularity and highmolecular weights. Polymerization carried out with the novel catalyst istruly living, with no reactive end transfer.

The novel catalyst contains a Ni center. In view of what other workershave suggested, it was surprising that aryl halides would even reactwith Ni(dppp)₂, as we used to make the novel catalyst.

Surprisingly, contrary to the report by Amatore et al. (1988) that Ni(0)complexes containing bidentate phosphine ligands do not react with arylhalides, we found that such reactions can indeed occur. The first suchreaction we investigated was the reaction between 2-bromobithiophene(Compound 3) and Ni(dppp)₂. We found that the reaction led to theformation of the Ni derivative 4. Compound 4 may be used as a highlyefficient catalytic initiator of controlled polymerization of Grignardmonomers such as compound 2, or of other organometallic monomers such asorganozinc monomers.

The novel catalyst is stable. Unlike some prior catalysts, it does notneed to be prepared in situ. Instead, the catalyst may be prepared insolution and stored in solution under refrigeration for weeks or months,to be used when needed.

The novel catalytic process gives 95% or greater regioregularity forsome polymerizations. Indeed, within resolving ability, essentially 100%regioregularity has been achieved for at least some polymers, forexample essentially 100% regioregular poly(3-alkylthiophene)s.Regioregularity gives rise to better electronic properties.

The concept of “regioregular” polythiophenes may be illustrated asfollows:

The above structure is a regioregular polymer. There is regular “R”group placement at the 3-positions of the thiophene rings, which tendsto enhance electronic properties.

The above structure is not a regioregular polymer. Irregular placementof the “R” groups, i.e. at random 3- and 4-positions on the thiophenerings, tends to diminish useful electronic properties such as electricalconductivity.

The novel catalyst sustains polymerization to unprecedentedly highmolecular weights. The limit of polymerization appears to be imposedsolely by the polymer's solubility. Higher molecular weight also tendsto improves electronic properties.

The product's molecular weight can be controlled by changing the amountof catalyst, e.g. catalyst 4, used in the polymerization. Thedistribution of molecular weights (the polydispersity) is typicallynarrow (less than 1.5), reflecting the living chain-growth character ofthe novel polymerization. The linear dependence of the molecular weightof polythiophene made from monomer 2 (FIG. 2A) is evidence of the livingchain-growth mechanism of polymerization.

Block co-polymers are readily synthesized with the novel catalysts.

The catalyst can be made inexpensively. It can be used in bothhomogeneous and heterogeneous reactions.

The catalytic initiators may be prepared by reaction of easily availablearyl halides (Ar—X, where Ar=substituted or unsubstituted thienyl, orsubstituted or unsubstituted phenyl; X=F, Cl, Br, I).

Exemplary embodiments of the invention include the following:

A method of synthesizing a catalyst, said method comprising reacting insolution Ar—X with NiL₂ wherein:

-   -   Ar denotes substituted or unsubstituted aryl;    -   L₂ denotes two bidentate ligands, wherein the two bidentate        ligands may be the same or different; and    -   X denotes a halogen.        A method as described, wherein:    -   Ar denotes a substituted or unsubstituted, fused or unfused        benzene, thiophene, pyrrole, or furan radical; and    -   L₂ denotes two substituted or unsubstituted diphosphines,        wherein the two substituted or unsubstituted diphosphines may be        the same or different.        A method as described, wherein:    -   Ar denotes bithiophen-2-yl;    -   each L₂ denotes 1,3-bis(diphenylphosphino)propane, and    -   X denotes bromine.        The catalyst produced by one of the methods described.        A process for synthesizing a polymer, said process comprising        polymerizing a first monomer X′-Ar′-MX″ in the presence of a        composition or catalyst as described, wherein:    -   X′ denotes a monovalent halide    -   Ar′ denotes substituted or unsubstituted aryl;    -   M denotes Mg or Zn; and    -   X″ denotes a monovalent halide.        A process for synthesizing a block copolymer, said process        comprising continuing the polymerization process as described        after a time with a second monomer X′-Ar″-MX″ wherein    -   Ar″ denotes substituted or unsubstituted aryl, wherein Ar″ is        different from Ar′; and    -   X′, M, and X″ are as previously defined; wherein each of X′, M,        and X″, respectively, may be the same or different in the first        and second monomers.        A process for synthesizing a polymer, said process comprising        polymerizing a first monomer X′-Ar′-MX″ in the presence of a        composition or catalyst as described, wherein:    -   X′ denotes a monovalent halide    -   Ar′ denotes substituted or unsubstituted aryl;    -   M denotes Mg or Zn; and    -   X″ denotes a monovalent halide.        A process for synthesizing a block copolymer, said process        comprising continuing the polymerization process as described        after a time with a second monomer X′-Ar″-MX″ wherein    -   Ar″ denotes substituted or unsubstituted aryl, wherein Ar″ is        different from Ar′; and    -   X′, M, and X″ are as previously defined; wherein each of X′, M,        and X″, respectively, may be the same or different in the first        and second monomers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) depicts the preparation of Ni(II) square-planar catalyticinitiator 1 according to the method of Senkovskyy et al. (2007) andBronstein et al. (2009). FIG. 1(B) depicts the preparation of the novelcatalytic initiator 4 by the novel method described here.

FIG. 2 (A) depicts the number average molecular weight (Me) and thepolydispersity index (PDI) of polythiophene P1 as a function of thepercentage conversion of monomer 2 (solid line=calculated data). FIG.2(B) depicts the M_(n) of polymer P1 as a function of polymerizationtime.

FIG. 3(A) depicts the preparation of block copolymers P2 and P3. FIG.3(B) depicts the preparation of polymer P4 and the end-group compositionas determined from MALDI-TOF data.

FIG. 4 depicts a portion of the MALDI-TOF spectrum for polymer P4, alongwith several peak assignments, to illustrate how the end-groupcomposition was determined.

FIGS. 5, 6, 7, 8, 9, 10, and 11 depict the preparation of catalyticinitiators in accordance with this invention, and their use incontrolled polymerizations, including their use as surface-boundcatalytic initiators to prepare surface-bound conjugated polymer films.

FIGS. 12(A), 12(B), and 12(C) depict UV/Vis absorption spectra for threeconjugated polymer films prepared by controlled polymerization.

MODES FOR CARRYING OUT THE INVENTION General Procedures

FIG. 1 depicts: (A) the preparation of a Ni(II) catalytic initiator 1according to the method of Senkovskyy et al. (2007) and Bronstein et al.(2009); and (B) the preparation of the novel Ni catalytic initiator 4 bythe novel method described here.

Example 1

All reactions were performed under an atmosphere of dry nitrogen (unlessmentioned otherwise). Melting points were determined in open capillariesand are uncorrected. Column chromatography was performed on silica gel(Sorbent Technologies, 60 Å, 40-63 μm) slurry packed into glass columns.Tetrahydrofuran (THF), ether, toluene, hexanes, and dichloromethane weredried by passing through activated alumina; and N,N-dimethylformamide(DMF) by passing through activated molecular sieves; using a PS-400Solvent Purification System from Innovative Technology, Inc. The watercontent of the solvents was periodically controlled by Karl Fischertitration (using a DL32 coulometric titrator from Mettler Toledo).Isopropylmagnesium chloride (2.0 M solution in THF) was purchased fromAcros Organics. All other reagents and solvents were obtained fromAldrich or from Alfa Aesar, and were used without further purification.¹H NMR spectra were recorded at 250 and 400 MHz and are reported in ppmdownfield from tetramethylsilane; ³¹P NMR spectra were obtained at 161MHz and are reported in ppm relative to 80% aqueous H₃PO₄ as an externalstandard. UV-visible spectra were recorded on a Varian Cary 50 UV-Visspectrophotometer. GPC analysis of polymers was performed with Agilent1100 chromatograph equipped with two PLgel 5 μm MIXED-C and one PLgel 5μm 1000 Å columns connected in series, using THF as a mobile phase, andcalibrated against polystyrene standards. High resolution mass spectrawere obtained at the LSU Department of Chemistry Mass SpectrometryFacility using the MALDI-TOF method with a terthiophene matrix. Atomicforce microscopy images were acquired with an Agilent 5500 (PicoPlus)system with PicoScan v. 5.3.3 software.

Example 2

The Ni(dppp)₂ reagent used in these reactions can be prepared, forexample, by the method of B. Corain el al., J. Organomet. Chem. 1971,28, 133-136. Briefly, to a vigorously stirred mixture of 1.50 g (5.84mmol) of nickel(II) bis(acetylacetonate) (Ni(acac)₂) and 4.82 g (11.7mmol) of 1,3-bis(diphenylphosphino)propane (dppp) in 80 ml of ether and15 ml of toluene, a solution of i-Bu₃Al (19.8 ml of 1.0 M solution inhexanes, 19.8 mmol) was added slowly over a 1 h period (by syringe pump)under Ar atmosphere. The resulting mixture was stirred at roomtemperature for 24 h. During this period the solution's color changedfrom bright green to bright red. The reaction mixture was leftunperturbed for an additional 24 h, and the resulting precipitate wasfiltered under argon, and washed with excess ether to give 3.5 g (68%)of the product as a bright-orange solid material, mp 281° C., decomp.(lit. mp 281-283° C.).

Example 3

An equimolar mixture of Compound 3 and Ni(dppp)₂ was stirred in tolueneat 40° C. The reaction was monitored by ³¹P NMR, which allows Ni(dppp)₂to be identified easily by its characteristic singlet at 12.8 ppm. Wewere disappointed that initially we did not observe any significant newsignals; those initial results seemed to indicate that no reaction wasoccurring, consistent with reports in the earlier literature. Wenevertheless allowed the reaction to continue running for longer times,and we noticed that the intensity of the 12.8 ppm singlet graduallydecreased, almost disappearing after 72 hours. If the decreasing 12.8ppm signal had resulted simply from thermal degradation of Ni(dppp)₂,then we should have observed new ³¹P NMR signals corresponding to thedegradation products, but no such new signals were seen. Theseobservations led us to conclude that Compound 3 and Ni(dppp)₂ hadreacted with one another to produce a stable paramagnetic product thatwould not be detected by ³¹P NMR.

Example 4

Surprisingly, we obtained completely regioregularpoly(3-alkylthiophene)s (nearly 100% regioregularity) with the novelprocess. For example, we obtained nearly 100% regioregularity by addinga catalytic amount of an in situ-prepared toluene solution of complex 4to a solution of Grignard monomer 2 in THF, and allowing the reaction toproceed for 1 hour at 35° C., followed by precipitation of the reactionmixture into methanol. The poly(3-hexylthiophene) (P3HT) compound P1(FIG. 1B) product was completely regioregular. Regioregularity, definedas the fraction of head-to-tail (HT) coupled 3-hexylthienyl units, wasclose to 100% as determined by ¹H NMR. The molecular weight of CompoundP1 was strongly dependent on the molar percentage of Complex 4 in thepolymerization mixture, consistent with a living chain-growth mechanism.

Example 5

FIG. 2 (A) depicts the number average molecular weight (M_(n)) and thepolydispersity index (PDI) of polymer P1 as a function of the percentageconversion of monomer 2 (solid line=calculated data). FIG. 2(B) depictsthe M_(n) of polymer P1 as a function of polymerization time.Polymerization was carried out with 0.25 mol % of Complex 4. M_(n) andPDI (M_(w)/M_(n)) were determined by gel permeation chromatographyrelative to polystyrene standards, and percent conversion of monomer 2was determined by ¹H NMR.

Example 6

Once a solution of Complex 4 had been prepared, it could be stored forat least a few weeks in a freezer without losing its catalytic activity.(We do not have data for longer storage times.) However, we have notbeen able to isolate Complex 4 as a solid state composition that retainscatalytic activity. Since paramagnetic Complex 4 was NMR-silent, therewas no easy way to quantify the amount of Complex 4 that was produced insitu from the reaction of Compound 3 and Ni(dppp)₂. We observed that ifCompound 3 and Ni(dppp)₂ were allowed to react for at least 72 hours (atime that corresponded to almost complete disappearance of the Ni(dppp)₂signal from the ³¹P NMR spectrum), then the molecular weight of CompoundP1 could be accurately predicted based on the initial amount of theNi(dppp)₂, an observation that was consistent with the essentiallycomplete conversion of Ni(dppp)₂ to Complex 4. In some instances wefound it more convenient to allow Compound 3 and Ni(dppp)₂ to react for24 hours, and in such a case the conversion to Complex 4 occurred with ayield around 60%, as determined by the molecular weight of the polymerP1 produced with the resulting catalytic solution.

Example 7

In multiple experiments, we have consistently prepared P3HT Compound P1with a number average molecular weight (M_(n)) ranging between 20 kDaand 80 kDa, depending on the molar fraction of catalytic Complex 4.Higher molecular weights were not produced under the particular reactionconditions we employed, likely due to the limited solubility of P3HThaving a molecular weight above 80 kDa. In all cases, the P3HT polymersproduced via Complex 4 had high regioregularity (close to 100%), and anarrow polydispersity index (PDI≦1.5). The number average molecularweight M_(n) of Polymer P1 was linearly dependent on the conversion ofGrignard monomer 2 (FIG. 2A), an observation that is consistent with aliving chain growth mechanism of polymerization.

Polymerization was rapid and efficient. Polymerization was practicallycomplete 20 minutes after the addition of Complex 4 to Grignard monomer2 (FIG. 2B). We could not detect any ³¹P NMR signals duringpolymerization. (For this experiment, polymerization was carried out inan NMR tube containing 5 mol % of Complex 4 in order to obtain a goodNMR signal). However, quenching the reaction mixture with methanolimmediately produced a broad ³¹P NMR signal at −20 ppm, corresponding tothe free dppp ligand.

Example 8

Using the activator Ni(dppp)₂ alone did not result in polymerization ofmonomer 2—only a very low (<5%) yield of P3HT was obtained, evenfollowing an extended reaction time. (We hypothesize that even in thiscase the polymerization was likely catalyzed not by Ni(dppp)₂ itself,but instead by a catalytic initiator analogous to Complex 4, formed byreaction between Ni(dppp)₂ and some residual, unreacted2,5-dibromo-3-hexylthiophene that had been used to prepare Grignardmonomer 2.) When Complex 4 was used as the catalytic initiator, thepresence of a bithiophene terminus in polymer P1 was unambiguouslyconfirmed by MALDI-TOF end-group analysis. These observations stronglysupported our hypothesis that Complex 4 was the initiating catalyticspecies for polymerization.

Example 9

A major difference between polymerization as initiated by Complex 4 andthat for conventional catalyst-transfer Kumada polymerization ofCompound 2, as catalyzed by Ni(dppp)Cl₂, was demonstrated by adding tothe reaction mixture TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), whichis a stable radical inhibitor. When polymerization of Grignard monomer 2was catalyzed by Ni(dppp)Cl₂ (0.3 mol %) in the presence of 1 mol %TEMPO, the reaction was unaffected by the presence of the radicalinhibitor. By contrast, adding the same amount of TEMPO to a reactionmixture containing 0.3 mol % of Compound 4 completely inhibitedpolymerization, and no polymer was produced.

Example 10

FIG. 3(A) depicts the preparation of block copolymers P2 and P3. FIG.3(B) depicts the preparation of polymer P4 and its end-group compositionas determined by MALDI-TOF data. FIG. 4 depicts a portion of theMALDI-TOF spectrum for polymer P4, along with several peak assignments.

Example 11

With a true “living” polymerization, block copolymers can beconveniently produced by sequentially adding different monomers to thereaction mixture, and allowing sufficient time in between for completereaction. For example, by adding Grignard monomers 2 and 5 to a solutionof the external catalytic initiator 4 (1 mol %) at 35° C., we preparedtwo completely regioregular block copolymers P2 and P3 (˜100% HTcoupling within each block). Copolymers P2 and P3 each had highmolecular weights, and both could be prepared with relatively shortpolymerization times. See FIG. 3(A).

Example 12

The composition of a polymer chain's end groups (e.g., as determined byMALDI-TOF analysis) can reveal details about the mechanism of itspolymerization. However, due to the similarity in molecular weights ofthe bithien-2-yl (biTh) end group (165 Da) and the 3-hexylthien-2,5-diylpolymer repeating unit (166 Da), MALDI-TOF did not permit unambiguousconfirmation that the bithiophene terminal unit from catalytic initiator4 had been incorporated into the P1 chain. To help resolve thisambiguity, we prepared a new polymer P4, poly(3-octylthiophene) (P3OT),by polymerizing Grignard monomer 6 in the presence of 0.3 mol % ofcatalytic initiator 4. See FIG. 3(B). Polymer P4 (M_(n) 57 kDa, PDI 1.5)was completely regioregular (essentially 100%). Because the molecularweight of the 3-octylthien-2,5-diyl repeating unit (194 Da) wassubstantially different from the molecular weight of the biTh unit, wewere able to confirm that the bithiophene terminal unit had beenincorporated into polymer P4. Mass spectrometry also confirmed that theterminal group at the other end of the polymer chain was predominantlyBr (i.e., P4 comprised mainly biTh-(P3OT)-Br chains). The predominanceof the Br terminal group contrasted with the H-termination that wouldtypically be observed in catalyst-transfer polymerization using atraditional Ni(II) catalyst.

Example 13

We wished to confirm whether the initial bromine atom from catalyticinitiator 4 was indeed transferred throughout the entire sequence ofchain growth steps to become a terminal atom in the resulting PTpolymer. To trace the fate of the initial bromine atom, we polymerized5-iodo-3-octyl-2-thienylmagnesium chloride, Grignard monomer 7, whichcontains an iodine atom and which was prepared from2,5-diiodo-3-octylthiophene. Using monomer 7 allowed us to use MALDI-TOFto distinguish between Br and I terminators at the end of the P5 chain.The MALDI-TOF analysis confirmed that a high fraction of polymer chainsterminated with bithiophene at one end, and with Br rather than with Iat the other end (i.e., biTh-(P3OT)-Br). The only potential source ofbromine atoms was from the catalytic initiator 4. The conclusion wasthat “halogen transfer” occurred during sequential monomer addition tothe reactive end of the growing polymer chain. The bromine atom was sostrongly associated with the reactive end of the chain that it prevailedover the large excess of iodide anion (from Grignard monomer 7).

Further Examples: Preparation of Catalytic Initiators for ControlledPolymerization of Halogenated Aromatic Grignard Reagents and their Usein Preparation of Conjugated Polymers Example 14

General Procedure for the Preparation of Catalytic Initiator 4.

2-Bromobithiophene (0.3 ml of 81.6 mM solution in toluene, 0.025 mmol)was added to a solution of 22 mg (0.025 mmol) of Ni(dppp)₂ in 10 ml oftoluene at room temperature. The resulting mixture was stirred at 40° C.for 48 h, after which it contained approximately a 2.5 mM concentrationof Compound 4. The solution could be stored in a freezer under inertatmosphere for at least 1 month without decreasing its catalyticactivity.

Example 15

Representative Procedure for Externally Initiated ControlledPolymerization: Polymer P1.

A solution of i-PrMgCl (0.75 ml of 2.0 M solution in THF, 1.5 mmol) wasadded dropwise to a stirred solution of 0.49 g (1.5 mmol) of2,5-dibromo-3-hexylthiophene in 22 ml of THF at 0° C., and the resultingsolution was stirred for 1 h at this temperature to yield a solution ofGrignard reagent 2. An aliquot of solution of 4 (1.8 ml of 2.5 mMsolution in toluene, 4.5 μmop was added to the Grignard reagent solutionat room temperature. The reaction mixture was stirred at 35° C. for 1 h.Precipitation into 120 ml of methanol resulted in a crude, dark-purplepolymer which was placed into a Soxhlet extractor, and extractedsuccessively with methanol, hexane, and CHCl₃. The chloroform fractionyielded 0.10 g (40%) of polymer P1 as a dark-purple solid, M_(n) 48 kDa,PDI 1.35 (GPC, vs. polystyrene). ¹H NMR (400 MHz, CDCl₃) δ 6.98 (s, 1H),2.80 (t, J=7.9 Hz, 2H), 1.78-1.64 (m, 2H), 1.49-1.29 (m, 6H), 0.91 (t,J=6.9 Hz, 3H).

Example 16

Block Copolymer P2.

A solution of i-PrMgCl (0.32 ml of 2.0 M solution in THF, 0.64 mmol) wasadded dropwise to a stirred solution of 0.2 g (0.62 mmol) of2,5-dibromo-3-hexylthiophene in 15 ml of THF at 0° C., and the resultingsolution was stirred for 1 h at this temperature to yield a solution ofGrignard reagent 2. An aliquot of a solution of catalytic initiator 4(2.5 ml of 2.5 mM solution in toluene, 6.2 μmop was added to theGrignard reagent solution, and the reaction mixture was stirred at 35°C. for 1 h. A solution of the Grignard reagent 5 (prepared separately at0° C. from 0.25 g (0.62 mmol) of2-[(2,5-dibromothiophen-3-yl)ethoxy]-tert-butyldimethylsilane in 30 mlof THF and 0.32 ml (0.64 mmol) of 2.0 M solution of i-PrMgCl in THF) wasadded dropwise over a period of 1 min, and the resulting solution wasstirred at 35° C. for additional 1.5 h. Precipitation into 150 ml ofmethanol resulted in a crude dark-purple polymer which was placed into aSoxhlet extractor, and extracted successively with methanol, hexane, andCHCl₃. The chloroform fraction yielded 0.087 g (37%) of block copolymerP2 as a dark-purple solid material, M_(n) 26 kDa, PDI 1.5 (GPC, vs.polystyrene). ¹H NMR (400 MHz, CDCl₃) δ 7.08 (s, 0.67H), 6.98 (s, 1H),3.91 (t, J=6.7 Hz, 1.33H), 3.04 (t, J=6.7 Hz, 1.33H), 2.81 (t, J=8.0 Hz,2H), 1.81-1.63 (m, 2H), 1.49-1.28 (m, 6H), 0.90 (s, 6H), 0.05 (s, 4H).Based on the ¹H NMR data, the ratio of P3HT topoly[3-(TBDMSO-ethyl)thiophene] blocks was ˜1.5:1.

Example 17

Block copolymer P3. A solution of i-PrMgCl (0.32 ml of 2.0 M solution inTHF, 0.64 mmol) was added dropwise to a stirred solution of 0.25 g (0.62mmol) of 2-[(2,5-dibromothiophen-3-yl)ethoxy]-tert-butyldimethylsilanein 25 ml of THF at 0° C., and the resulting solution was stirred for 1 hat this temperature to yield a solution of Grignard reagent 5. Analiquot of initiator solution 4 (2.5 ml of 2.5 mM solution in toluene,6.2 □mol) was added to the Grignard reagent solution, and the reactionmixture was stirred at 35° C. for 1 h. A solution of Grignard reagent 2(prepared separately at 0° C. from 0.2 g (0.62 mmol) of2,5-dibromo-3-hexylthiophene in 22 ml of THF and 0.32 ml (0.64 mmol) of2.0 M solution of i-PrMgCl in THF) was added dropwise over a period of 1min, and the resulting solution was stirred at 35° C. for additional 1.5h. Precipitation into 150 ml of methanol resulted in a crude,dark-purple polymer which was placed into a Soxhlet extractor, andextracted successively with methanol, hexane, and CHCl3. The chloroformfraction yielded 0.073 g (30%) of block copolymer P3 as a dark-purplesolid material, M_(n) 48 kDa, PDI 1.4 (GPC, vs. polystyrene). ¹H NMR(400 MHz, CDCl₃) δ 7.08 (s, 0.67H), 6.98 (s, 1H), 3.91 (t, J=6.7 Hz,1.33H), 3.04 (t, J=6.8 Hz, 1.33H), 2.81 (t, J=8.0 Hz, 2H), 1.81-1.63 (m,2H), 1.49-1.28 (m, 6H), 0.90 (s, 6H), 0.05 (s, 4H). Based on ¹H NMR, theratio of P3HT to poly[3-(TBDMSO-ethyl)thiophene] blocks was ˜1.5:1.

Example 18

Polymer P4 was prepared following the representative procedure forpolymer P1, starting from 0.25 g (0.7 mmol) of2,5-dibromo-3-octylthiophene in 11 ml of THF, 0.35 ml of 2.0 M solutionof i-PrMgCl in THF (0.7 mmol), and using 0.85 ml of 2.5 mM solution ofthe catalytic initiator 4 in toluene (2.1 μmol). Purification of thecrude polymer using Soxhlet extraction yielded 0.04 g (30%) of P4 as adark-purple solid material, M_(n) 57 kDa, PDI 1.5 (GPC, vs.polystyrene). ¹H NMR (250 MHz, CDCl₃) δ 6.97 (s, 1H), 2.80 (t, J=7.8 Hz,2H), 1.84-1.59 (m, 2H), 1.56-1.05 (m, 10H), 1.01-0.75 (m, 3H).

Example 19

Polymer P5 was prepared following the representative procedure givenabove for polymer P1, starting from 0.2 g (0.45 mmol) of2,5-diiodo-3-octylthiophene in 11 ml of THF, 0.22 ml of 2.0 M solutionof i-PrMgCl in THF (0.45 mmol), and using 0.53 ml of 2.5 mM solution ofthe catalytic initiator 4 in toluene (1.33 μmol). Purification of thecrude polymer using Soxhlet extraction yielded 0.016 g (19%) of polymerP5 as a dark-purple, solid material, M_(n) 9 kDa, PDI 1.5 (GPC, vs.polystyrene). ¹H NMR (250 MHz, CDCl₃) δ 6.97 (s, 1H), 2.80 (t, J=7.8 Hz,2H), 1.84-1.59 (m, 2H), 1.56-1.05 (m, 10H), 1.01-0.75 (m, 3H).

Catalytic initiators were prepared by reacting an aryl halide withexcess nickel-ligand complex at slightly elevated temperature in toluene(or other suitable solvent) for 24-72 h. See FIG. 5.

The catalytic initiators can be stored under refrigeration in solutionfor at least one month. They can be used as external catalyticinitiators in the preparation of various conjugated polymers and blockcopolymers through controlled polymerization of Grignard monomers orfunctionalized Grignard monomers. The polymerization involves addingcatalytic initiator solution (from about 0.01 mol-% to about 1 mol-% (orhigher) active catalyst, depending on the desired molecular weight ofthe polymer) to a solution of the Grignard monomer, and allowing thecomponents to react at about 25° C. to about 35° C. with stirring(typically for about 1 hour). If a block copolymer is desired, then asecond Grignard monomer can be added after a time, allowed to react foran additional period, and so forth. Following polymerization, the crudepolymer is precipitated into methanol, and is purified (e.g. by Soxhletextraction).

Alternatively, if an R group in catalytic initiator I or II includes ananchoring group for chemical attachment to a surface (e.g., to a surfaceof silica, glass, metal oxide, polymer, etc.), then the anchor can beused to initiate surface-confined polymerization to produce asurface-attached, conjugated polymer film or brush. Such films can beused, for example, in electronic applications. See, e.g., FIGS. 5 and 6.In many cases, structures made with polymers in accordance with thepresent invention cannot be made by more traditional methods, such asmelting, extrusion, solution spin-casting, or ink-jet printing. Theymay, however, be directly “cast” from solution via surfacepolymerization in accordance with the present invention.

FIGS. 7, 8, 9, 10, and 11 depict examples of catalytic initiators, e.g.,compounds 4 and 8, and their use in the preparation of regioregularpolymers—e.g., poly(3-hexylthiophene) P1, poly(3-octylthiophene) P4;block copolymers—e.g., P2 and P3; surface-attached films ofpolymers—e.g., polythiophene P6, poly(p-phenylene) P7; surface-attachedfilms of block copolymers—e.g., P8 and P9; and surface-attached films ofcopolymers—e.g., P10.

An optional feature of the novel controlled polymerization method isthat it permits the polymerization of “oligomeric” monomers (i.e.,monomers that contain more than one aromatic unit). This option isespecially useful for surface-confined polymerization, which isintrinsically more difficult due to the heterogeneous nature of mostsurfaces; and it is also useful for the preparation of copolymers.Examples of such preparations are thin films of polythiophene P6,prepared from monomers 9 and 10, and thin films of copolymer P10prepared, from monomer 11.

Example 20

Polymerization Initiator 8.

A mixture of 44 mg (0.05 mmol) of Ni(dppp)₂ and 9.0 mg (0.025 mmol) of2-triethoxysilyl-5-iodothiophene in 10 ml of toluene was stirred at 40°C. for 12 h, and the resulting solution (in which the nominalconcentration of compound 8 was 2.5 mM) was used for surfaceimmobilization without further purification.

Example 21

Activation of Quartz Substrates.

Rectangular quartz slides (approx. 1.1×2.5 cm²) were ultrasonicatedsequentially for 10 minutes each in CHCl3, methanol, and deionizedwater. These ultrasonicated slides were then placed into a Piranhasolution (a mixture of conc. H₂SO₄ and 30% H₂O₂ (7:3)) andultrasonicated for an additional 30 min. After rinsing with copiousamounts of deionized water, the quartz substrates were dried in N₂ flowat room temperature for 4 h, and then activated using O₂ plasma for 10min.

Example 22

Preparation of Surface-Immobilized Initiator 8a.

Activated quartz slides were immersed into a solution of polymerizationcatalytic initiator 8 in toluene and kept at 60° C. for 3 days followedby gentle rinsing with anhydrous toluene. Due to the air-sensitivenature of the compounds involved, all procedures were carried out insidea glove box.

Example 23

Representative Procedure for Preparation of Conjugated Polymer Films bySurface-Initiated Polymerization Using Initiator 8: Preparation ofPolythiophene P6 Thin Films.

Quartz substrates were first modified with an initiator 8a monolayer,and then were immersed in a 0.1 M solution of Grignard monomer((5-bromothien-2-yl)magnesium chloride) in THF (prepared from 0.24 g(1.0 mmol) of 2,5-dibromothiophene in 10 ml of THF and 0.5 ml of 2.0 Msolution of i-PrMgCl (1.0 mmol)). The reaction mixture was gentlystirred for 16 hours at 40° C., and the substrates were rinsed withanhydrous toluene. Then the PT-covered substrates were immersed in a 5mM solution of Ni(dppp)₂ in toluene for 1 day. After residual Ni(dppp)₂was removed by washing with anhydrous toluene three times, theregenerated thin films were again immersed in a 0.1 M solution ofGrignard monomer in THF with gentle stirring for 16 h at 40° C. At theend of the reaction period, the reactive Ni centers were quenched byplacing the substrates into methanol and ultrasonicating for 10 min. Theresulting PT thin films were further cleaned by ultrasonication in CHCl₃(2×10 min).

Example 24

Preparation of a Thin Film of Block Copolymer P8.

Quartz substrates were first modified with initiator 8a monolayer andthen immersed in a 0.03 M solution of 4-iodophenylmagnesium chloride(prepared from 0.10 g (0.3 mmol) of 1,4-diiodobenzene and 0.15 ml of 2.0M solution of i-PrMgCl (0.3 mmol) at 0° C.) at 25° C. for 12 h withgentle stirring. Then the substrate was rinsed with toluene and immersedin a 5 mM solution of Ni(dppp)₂ for 8 h. After residual Ni(dppp)₂ wasremoved by washing with toluene, the substrate was placed in a 0.05 Msolution of (5-bromothien-2-yl)magnesium chloride (prepared from 0.12 g(0.5 mmol) of 2,5-dibromothiophene in 10 ml of THF and 0.25 ml of 2.0 Msolution of i-PrMgCl (0.5 mmol) at 0° C.) at 25° C. for 8 h with gentlestirring. At the end of the polymerization, the substrate was placed inmethanol and ultrasonicated for 10 min, followed by ultrasonication inCHCl₃ (2×10 min).

Example 25

Preparation of a Thin Film of Copolymer P10.

This polymerization was carried out following the representativeprocedure described above for thin films of polymer P6, using Grignardmonomer 11, which had been prepared by reacting equimolar amounts of2,5-bis(5-bromothien-2-yl)-3,4-dioxythiophene and i-PrMgCl. Thepolymerization was carried out at 45° C. for 12 h.

Example 26

Characterization of the Thin Films.

The thin films of conjugated polymers and copolymers were characterizedby UV/Vis absorption spectroscopy and Atomic Force Microscopy (AFM). Theresults indicated that the films had high density and a uniform surfacemorphology. The representative UV/vis absorption spectra for polymersP6, P8 and P10 (prepared as described above, P6 prepared from(5-bromothien-2-yl)magnesium chloride monomer) are shown in FIGS. 12(A),12(B) and 12(C). The UV/Vis spectra confirmed that dense and thick filmsof the polymers had been prepared. The AFM images (not shown) confirmedthat the surface had been uniformly covered by polymer.

The complete disclosures of all references cited in this specificationare hereby incorporated by reference, including the complete disclosureof the 61/503,727 priority application. Also incorporated by referenceare the complete disclosures of the following abstracts andpresentations by the inventors and their colleagues: (1) Hwang, E.;Choi, J.; Lusker, K. L.; Garno, J. C.; Nesterov, E. E. “Nanopatternedpolythiophene thin films prepared by surface-initiated polymerization.”International Chemical Congress of Pacific Basin Societies (Pacifichem2010), Honolulu, Hi., 2010. Abstr. 33 (Dec. 15-20, 2010; Abstractpublished Jul. 12, 2010); (2) Choi, J.; Nesterov, E. E. “Highlyefficient externally initiated Kumada polycondensation: controlledpreparation of complex polythiophene architectures.” InternationalChemical Congress of Pacific Basin Societies (Pacifichem 2010),Honolulu, Hi., 2010. Abstr. 1192 (Dec. 15-20, 2010; Abstract publishedJul. 12, 2010); (3) Choi, J.; Daniels, S. L.; Garno, J. C. Nesterov, E.E. “Supramolecular organization in stimuli-responsive amphiphilicconjugated polythiophene block copolymers.” 66th Southwest and 62ndSoutheast ACS Regional Meeting, New Orleans, L A, 2010. Abstr. SESW-1017(Nov. 30-Dec. 4, 2010; Abstract published approximately November 2010);(4) Hwang, E.; Choi, J.; Lusker, K. L.; Garno, J. C.; Nesterov, E. E.“Nanopatterned surface-immobilized polythiophene thin films by surfaceinitiated metal-catalyzed living polymerization.” 66th Southwest and62nd Southeast ACS Regional Meeting, New Orleans, L A, 2010. Abstr.SESW-478 (Nov. 30-Dec. 4, 2010; Abstract published approximatelyNovember 2010); (5) Lusker, K. L.; Hwang, E.; Nesterov, E. E.; Garno, J.C. “Nanopatterns as selective sites for surface chemical reactions.”66th Southwest and 62nd Southeast ACS Regional Meeting, New Orleans, LA, 2010. Abstr. SESW-375 (Nov. 30-Dec. 4, 2010; Abstract publishedapproximately November 2010); (6) Choi, J.; Nesterov, E. E. “Preparationof polythiophene block-copolymers incorporating low energy gap groupusing nickel catalyzed quasi-living polymerization.” 239th ACS NationalMeeting, San Francisco, Calif., 2010. Abstr. POLY-284 (Mar. 21-25, 2010;Abstract published approximately February-March 2010); (7) Jinwoo Choi“Semiconducting Polymers and Block Copolymers Prepared by Chain-GrowthLiving Polymerization” (PhD dissertation, Louisiana State University,Baton Rouge, La., August 2011); and (8) Euiyong Hwang “Surface-InitiatedPolymerization as a Novel Strategy towards Preparation of OrganicSemiconducting Polymer Thin Films” (PhD Dissertation, Louisiana StateUniversity, Baton Rouge, La. May 2011). Where applicable, theseincorporations by reference include any supplemental material associatedwith a particular publication. In the event of an otherwiseirreconcilable conflict, however, the present specification shallcontrol. E.g., there are certain portions of the present specificationthat supersede certain portions of the provisional priority disclosure.

What is claimed:
 1. A process for synthesizing a polymer, said processcomprising polymerizing a first monomer X′-Ar′-MX″ in the presence of acatalyst; wherein: X′ denotes a monovalent halide; Ar′ denotessubstituted or unsubstituted aryl; M denotes Mg or Zn; X″ denotes amonovalent halide; the catalyst comprises a complex ArNiLX; Ar denotessubstituted or unsubstituted aryl; L denotes a bidentate ligand; Xdenotes a monovalent anion; and X, X′, and X″ may be the same ordifferent.
 2. The process of claim 1, wherein the catalyst is covalentlybound to a surface via a linker moiety, whereby the resulting polymer iscovalently bound to the surface.
 3. The process of claim 2, wherein thelinker moiety is selected from the group consisting of silyl,phosphonate, carboxylate, and (CH₂)_(n).
 4. The process of claim 1,wherein the resulting polymer has 95% or greater regioregularity.
 5. Aprocess for synthesizing a block copolymer, said process comprisingcontinuing the polymerization process of claim 1 after a time with asecond monomer X′-Ar″-MX″ wherein Ar″ denotes substituted orunsubstituted aryl, wherein Ar″ is different from Ar′; and X′, M, and X″are as previously defined; wherein each of X′, M, and X″, respectively,are identical or nonidentical in the first and second monomers.
 6. Theprocess of claim 1, wherein: Ar denotes substituted or unsubstituted,fused or unfused benzene, thiophene, pyrrole, or furan, L denotessubstituted or unsubstituted diphosphine; and X denotes a monovalenthalide.
 7. The process of claim 1, wherein: Ar denotes bithiophen-2-yl;L is 1,3-bis(diphenylphosphino)propane; and X denotes bromide.
 8. Theprocess of claim 1; additionally comprising the step of synthesizing thecatalyst by reacting in solution Ar—X with NiL₂, wherein X is a halogen.9. The process of claim 8, wherein: Ar denotes substituted orunsubstituted, fused or unfused benzene, thiophene, pyrrole, or furan,and L₂ denotes two identical or nonidentical, substituted orunsubstituted diphosphines L.
 10. The process of claim 8, wherein: Ardenotes bithiophen-2-yl; each L is 1,3-bis(diphenylphosphino)propane,and X denotes bromine.
 11. The process of claim 8, additionallycomprising the step, after the catalyst is synthesized and before thepolymer is synthesized, of storing the catalyst in solution.
 12. Theprocess of claim 11, wherein the catalyst is stored in solution underrefrigeration.
 13. The process of claim 12, wherein the catalyst isstored in solution under refrigeration for at least one month after thecatalyst is synthesized and before the polymer is synthesized.